1. Field of the Invention
The present invention generally relates to a wind power turbine and, more particularly, to a wind power turbine having both drag-type and lift-type blades for improving electricity generating efficiency thereof.
2. Description of the Related Art
There are two types of blades for wind power turbines based on different operation manners of the blades, such as drag type and lift type. The drag-type blades have smaller starting torque, which makes it easy to drive the blades to rotate when in a slow wind speed but results in lower wind power conversion rate when in a fast wind speed. In contrast, the lift-type blades have larger starting torque when in the slow wind speed, but have better electricity generating efficiency when in the fast wind speed. Thus, based on a combination of both types of blades, the drag-type blades may drive the life-type blades to rotate when in the slow wind speed and the lift-type blades may improve the wind power conversion rate for better electricity generating efficiency when in the fast wind speed.
FIG. 1 shows a conventional wind power turbine having both the drag-type and lift-type blades. The wind power turbine includes a drag-type fan 7, a lift-type fan 8 and a base 9. The drag-type fan 7 has a shaft 71 having a plurality of drag-type blades 72 coupled to an outer circumference of the shaft 71. The lift-type fan 8 has a plurality of lift-type blades 81 connected to the shaft 71 via a plurality of connection members 82. In this way, the drag-type fan 7 and the lift-type fan 8 may rotate in a synchronous manner. The base 9 has an electricity generator 91 which includes a rotor and a stator (not shown), with one end of the shaft 71 being rotatably coupled with the base 9 and connected to the electricity generator 91. Thus, the base 9 may support the drag-type fan 7 and the lift-type fan 8 for rotation. Based on this, when the wind drives the drag-type fan 7 and the lift-type fan 8 to rotate, the rotor of the electricity generator 91 may rotate synchronously with the shaft 71, allowing electricity to be generated due to magnetic induction between the rotor and the stator of the electricity generator 91. Thus, electricity generation by wind power is achieved.
However, each drag-type blade 72 has a windward face and a leeward face. When a forward rotation torque is generated as the wind blows over the windward face of one drag-type blade 72, a reversed rotation torque is simultaneously generated as the wind also blows over the leeward face of the other drag-type blade 72. As a result, the reversed rotation torque may offset a portion of the forward rotation torque, leading to a lower wind power conversion rate. Thus, electricity generating efficiency of the electricity generator 91 is impacted.
For the lift-type blades 81, a rotation torque is generated due to a difference in the speed of wind passing through the inner and outer faces of the lift-type blades 81. However, the lift-type blade 81 is usually in the form of a plate with even thickness or in the form of a cambered plate. Alternatively, the lift-type blade 81 may have a drip-like cross section. These forms of the lift-type blade 81 appear to have a symmetric pattern, resulting in a small difference in the speed of wind passing through the inner and outer faces of the lift-type blades 81. Thus, electricity generation efficiency by wind power is low.